1. Field of the Invention
The present invention relates to a highly hydrophilic and porous sintered body made of a thermoplastic polyacrylonitrile resin.
2. Prior Art
Many proposals have been conventionally made to produce an open-cellular porous sintered body prepared from a pulverulent thermoplastic resin.
For example, Japanese Patent Publication No. 6385/1957 discloses a method of producing a porous sintered body of polyethylene by heating to sinter a pulverulent polyethylene at a temperature of from 100.degree. C. to the temperature at which decomposition and/or gelation of the polyethylene does not occur. Japanese Patent Publication No. 5435/1958 discloses a method of producing a porous sintered body of polyethylene by heating to sinter a pulverulent polyethylene having a molecular weight of more than 75,000 at a temperature of higher than 120.degree. C. However, these prior art sintered bodies of polyethylene are non-hydrophilic and hence not suited as the materials for manufacturing filters, inking rollers and tips of sign pens which require hydrophilic properties. Moreover, these prior art sintered bodies are inferior in porosity and hardness.
Japanese Patent Publication No. 2582/1961 discloses a method of producing a porous sintered article comprising the steps of heating a pulverulent linear polyamide at a temperature of higher than 250.degree. F. and lower than the melting point of the polyamide, cold-pressing after cooling, and then sintering the thus pressed article in a non-oxidative atmosphere. However, this prior art sintered body of polyamide is feebly hydrophilic and has the disadvantage that difficulties are encountered in the sintering operation since the melting point of the polyamide is relatively high and it tends to decompose when heated to a temperature near the melting point thereof. A further disadvantage of such sintered body of polyamide is the difficulty in producing a sintered article having open-cellular pores.